1. Field of the Invention
This invention relates to a recording apparatus in which a light beam modulated by modulation signal is thrown upon a recording medium to thereby effect recording thereon.
2. Description of the Prior Art
If such an arrangement is made that coherent light provided from a laser oscillator or the like is applied to an ultrasonic wave modulator and a primary light resulting from the application of ultrasonic signal to the ultrasonic wave modulator emerges outwardly but a zero-order light resulting when the ultrasonic signal is not applied to the ultrasonic wave modulator does not emerge outwardly and that the primary light emergent from such modulator is thrown upon a recording medium, then it is possible to record information on the recording medium by controlling the ultrasonic wave modulator by recording signals.
If primary light is so used for the recording, the ratio of the quantity of light thrown upon the recording medium during the application of ultrasonic signal to the ultrasonic wave modulator to the quantity of light thrown upon the recording medium during non-application of ultrasonic signal to the ultrasonic wave modulator (the extinction ratio) may be secured at a great value (easily at a value above 50) and therefore, this is suitable for a medium such as silver salt film having a low .gamma. value to be used as the recording medium.
However, the primary light obtained is only 60 to 70% of the input light to the ultrasonic wave modulator and this means a great loss of energy. Accordingly, it becomes necessary to provide a laser beam generator having a great output or to slow down the speed at which information is written in the recording medium.
The angle of separation .theta. between the zero-order light and the primary light from the ultrasonic wave modulator depends on the ultrasonic frequency and further on the laser wavelength. Therefore, where the laser in use is an argon ion laser, if multimode oscillation is effected, laser oscillations of eight different wavelengths occur simultaneously between 4579 A and 5145 A as the main oscillation wavelength. If such laser light is passed through an ultrasonic wave modulator, the primary diffracted light emergent therefrom is directed in eight different directions in accordance with the respective wavelength. Thus, where such primary diffracted light emergent in eight different directions is utilized as light energy in ON state, and if it is condensed by a condenser lens, the spot diameter of the beam becomes more enlarged than the spot diameter of a single wavelength. This means a poorer resolving power of the recording.